THE NATURAL REGIONS OF INDIA.—In dividing India into natural regions it is obvious that physical conditions must first be con sidered. The mountainous borderlands, the Indo-Gangetic plain, and the plateau of peninsular India form three entirely distinct areas, the economic development of each of which is quite unlike that of the others. The first of these—the mountainous border lands--must be further divided. It has already been shown that there are considerable physical differences between the Himalayas and the frontier regions of the north-west. The position of each with regard to the monsoon current, moreover, has led to a heavy rainfall in the one, and to a very low rainfall in the other, and as a result each has its distinctive vegetation.
Physically, the Indo-Gangetic plains seem to form one natural region, but it is impossible to neglect the influence of great rivers, like the Indus and the Ganges with their tributaries, which tend to give a distinct individuality to the countries through which they flow. It is better, therefore, to recognise the Indus plain and the Ganges plain (including that of the Brahmaputra) as separate natural regions, each of which must be further subdivided according to differences in physical structure, humidity, vegetation, and potentialities for economic development.
The whole of the Ganges plain is composed of alluvium, but to the west of the great bend at Rajmahal the rivers have generally sufficient velocity to carry off their silt, while to the east the slope is so gentle that they are in many cases unable to do so. Flooding consequently takes place, and the surface of the land consists of recent alluvium. In the west, on the other hand, old alluvial soil prevails. A further subdivision, based chiefly upon rainfall, may
be made. West of Allahabad the old alluvial soils have generally a rainfall of less than 40 inches, while to the east of Allahabad the precipitation is between 40 and 50 inches. On the recent alluvium, as far east as the Brahmaputra, between 50 and 75 inches of rain fall, while beyond that river the amount is from 75 to 100 inches.
Physically the Indus plain is not unlike that of the Ganges, but in climate and vegetation it differs to a great extent. The influence of the monsoon is slight, except in the northern plains of the Punjab, where along a comparatively narrow belt, which really forms an extension of the western division of the Ganges plain, and which stretches from the Jumna to the Jhelum, the rainfall varies from 40 inches in the east to 15 or 20 inches in the west. To the west and south-west lies a dry area with a rainfall from 5 to 15 inches, or even less. For a discussion of economic potentialities, this region may be divided. In the basins of the rivers forming the Panjnad, and in that of the Indus, a certain amount of settlement, based on irrigation from rivers or wells, is possible, but in the Thar or Indian desert a small nomadic population is all that can find subsistence.
The third great physical region is that of peninsular India. Here the east and west coastal plains may be distinguished by their topography and climate from the Deccan proper, where the region covered by the Black Soil, the north-eastern Archaean area with its high rainfall, and the southern Archaean area with its low rainfall, must all be treated separately.